U.S. patent number 4,533,814 [Application Number 06/462,475] was granted by the patent office on 1985-08-06 for laser pipe welder/cutter.
This patent grant is currently assigned to United Kingdom Atomic Energy Authority. Invention is credited to Brooke A. Ward.
United States Patent |
4,533,814 |
Ward |
August 6, 1985 |
Laser pipe welder/cutter
Abstract
A laser pipe welder/cutter for use where a pipe to be welded or
cut cannot be rotated, consisting of a focusing head mounted on a
carriage which runs on a track surrounding a hole in a base plate
through which a section of pipe to be operated upon can project.
The focusing head is arranged to maintain the laser beam at normal
incidence to the pipe as it traverses around the pipe and is linked
to a laser source via a flexible laser beam guide which consists of
at least two rigid sections joined by optical elbow joints which
permit motion about two mutually perpendicular axes, the lengths of
the rigid sections being such that the laser focusing head can
traverse more than a full circle around the pipe without the rigid
sections of the laser beam guide coming into contact with the
pipe.
Inventors: |
Ward; Brooke A. (Goring on
Thames, GB2) |
Assignee: |
United Kingdom Atomic Energy
Authority (London, GB2)
|
Family
ID: |
10528311 |
Appl.
No.: |
06/462,475 |
Filed: |
January 31, 1983 |
Foreign Application Priority Data
|
|
|
|
|
Feb 12, 1982 [GB] |
|
|
8204249 |
|
Current U.S.
Class: |
219/121.64;
219/121.63; 219/121.67; 219/121.72; 219/121.77; 219/121.79; 901/42;
901/47 |
Current CPC
Class: |
B23K
26/282 (20151001); B23K 26/103 (20130101) |
Current International
Class: |
B23K
26/10 (20060101); B23K 027/00 () |
Field of
Search: |
;219/121LC,121LD,121LN,121LG,121LS,121LT,121LU,121LV
;901/6,42,47 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Albritton; C. L.
Attorney, Agent or Firm: Hinds; William R.
Claims
I claim:
1. A laser processing apparatus comprising, a focusing head which
is mounted on a carriage which is adapted to follow a closed path
around a position at which a stationary workpiece to be processed
by a laser beam may be placed whilst maintaining the laser beam at
normal incidence to the workpiece and bringing it to a focus at the
surface of the workpiece, a flexible laser beam guide connecting
the focusing head to a stationary laser beam guide, the flexible
laser beam guide including at least three optical elbow joints each
having an angular movement of more than two hundred and seventy
degrees and means for reflecting the laser beam from one optical
elbow joint to another and thence to the focusing head, a first of
the optical elbow joints being associated with the focusing head, a
second of the optical elbow joints being associated with the fixed
laser beam guide and the third optical elbow joint being
intermediate the first and second optical elbow joints and
separated from them by distances such that the focusing head can
traverse more than a full circuit around the workpiece without the
flexible beam guide coming into contact with the workpiece.
2. A laser processing apparatus according to claim 1, wherein the
second optical elbow joint is provided with a rotational capability
about an axis which is coincident with that of the portion of the
fixed laser beam guide to which it is attached, and the focusing
head carriage is constrained to move on a track which is mounted on
a single axis gimbal frame which is pivoted about the same axis
thus enabling the laser beam to act on a workpiece which has its
axis at any orientation in a plane at right angles to the gimbal
axis.
3. A laser processing apparatus according to claim 1 or claim 2,
wherein each optical elbow joint includes a mirror in a mounting
which is adapted to be moved about two perpendicular axes, means
for sensing the position of a laser beam traversing the optical
elbow joint in relation to the optical axis of the optical elbow
joint and generating electrical signals related thereto, and a
servo mechanism arranged to vary the orientation of the movable
mirror to cause the path of the laser beam to be co-axial with the
optical axis of the optical elbow joint.
Description
The present invention relates to a device for carrying out
processing operations on a workpiece by means of a laser in
circumstances when it is not practicable to rotate the workpiece to
present different portions of its surface to the laser beam to be
operated upon.
There are a number of laser materials processing applications, such
as welding or cutting, which require the focus of a laser beam to
be moved circumferentially around a cylindrical workpiece which
cannot be rotated to present different parts of its surface to the
laser beam. One such application is the welding together of
sections of piping on site to form a continuous pipeline. In such a
case it is not possible to rotate the workpiece, and the focusing
head for the laser beam must be moved around the clamped butt
joints of two sections of pipe. The laser beam must be maintained
at near normal incidence to the surface of the pipe and moved
around it by more than a complete circle so as to ensure that the
weld is complete. The same requirement exists if the laser beam is
to be used to cut a length of pipe in two.
According to the present invention there is provided a laser
processing apparatus comprising, a focusing head which is mounted
on a carriage which is adapted to follow a closed path around a
position at which a stationary workpiece to be processed by the
laser beam may be placed whilst maintaining the laser beam at
normal incidence to the workpiece and bringing it to a focus at the
surface of the workpiece, a flexible laser beam guide connecting
the focusing head to a stationary laser beam guide, the flexible
laser beam guide including at least three optical elbow joints each
having an angular movement of more than two hundred and seventy
degrees and means for reflecting the laser beam from one optical
elbow joint to another and thence to the focusing head, a first of
the optical elbow joints being associated with the focusing head, a
second of the optical elbow joints being associated with the fixed
laser beam guide and the third optical elbow joint being
intermediate the first and second optical elbow joints and
separated from them by distances such that the focusing head can
traverse more than a full circuit around the workpiece without the
flexible beam guide coming into contact with the workpiece.
In one form of the invention, the second optical elbow joint is
provided with a rotational capability about an axis which is
coincident with that of the portion of the fixed laser beam guide
to which it is attached, and the focusing head carriage is
constrained to move on a track which is mounted on a single axis
gimbal frame which is pivoted about the same axis thus enabling the
laser beam to act on a workpiece which has its axis at any
orientation in a plane at right angles to the gimbal axis.
The invention will now be described by way of example, with
reference to the accompanying drawings, in which:
FIG. 1 is a schematic representation of a pipe welding or cutting
apparatus embodying the invention;
FIG. 2 illustrates the action of the apparatus of FIG. 1;
FIG. 3 is a longitudinal section of a type of optical elbow joint
which can be incorporated in the apparatus of FIG. 1; and
FIG. 4 is a longitudinal section of a second type of optical elbow
joint which can be incorporated in the apparatus of FIG. 1.
Referring to FIG. 1, an orbital laser welder/cutter consists of a
focusing head 1 which is mounted on a carriage 2 which runs on a
track 3 which surrounds a hole 4 in a base plate 5. The base plate
5 is in turn mounted on trunnions 6 which form part of a supporting
structure 7. The supporting structure 7 acts as a single axis
gimbal frame. The focusing head 1 is fixed to the carriage 2 in a
position such that a radial alignment of the focusing head 1 is
maintained as the carriage 2 moves around the track 3. A flexible
laser beam guide, shown generally by the numeral 8 connects the
focusing head 1 to a fixed laser beam guide 9. The fixed portion of
the laser beam guide 9 passes through the centre of one of the
trunnions 6. For protective purposes, the flexible laser beam guide
8 is provided with an articulated outer casing 10. The flexible
laser beam guide 8 includes three elbow joints 11, 12 and 13. The
elbow joint 11 conveys light to the focusing head 1, the elbow
joint 12 connects the flexible laser beam guide 8 to the fixed
laser beam guide 9, and the elbow joint 13 is intermediate the
other two elbow joints. Corresponding articulation is provided in
the outer casing 10. The elbow joints 11, 12 and 13 will be
described in more detail later. Each elbow joint is universal in
its action with an angular movement of more than 270.degree.. This,
coupled with the separation between the pairs of elbow joints 11
and 13 and 12 and 13, respectively, enables the focusing head 1 to
travel more than a full circle around the track 3 without the
flexible beam guide 8 coming into contact with a workpiece
projecting through the hole 4 in the base plate 5.
For example, to provide for the welding or cutting of a workpiece
in the form of piping 20 with a nominal diameter of 40 units
passing through the hole 4 in the base plate 5, the axis of
rotation of the elbow joint 11 perpendicular to the plane of the
base plate 5 should move around a circle of radius 70 units centred
on the hole 4 in the base plate 5, the corresponding axis of
rotation of the elbow joint 12 should be 110 units from the centre
of the hole 4 in the base plate 5, and the separations between the
corresponding axes of rotation of the elbow joints 11 and 13 and 12
and 13, respectively, should be 132.9 and 92.9 units.
The action of a flexible beam guide 8 with such dimensions is
illustrated in FIG. 2. As the action of the flexible laser beam
guide 8 is symmetrical, only half a complete circuit is shown. The
motion starts from the position labelled I, proceeds to position
II, and thence to position III. The remaining part of the motion is
a mirror image of that shown. The starting position is such that
the optic axis 21 of the focusing head 1 rotates through some
370.degree. in a complete cycle of operation, so ensuring the
complete joining or severance of sections of piping 20.
FIG. 3 shows the construction of one form of elbow joint. In this
form of elbow joint, an input mirror 31 and an output mirror 32 are
mounted in input and output parts 33 and 34, respectively, of the
elbow joint. The input and output parts 33 and 34 of the elbow
joint are joined by a short intermediate section 35 which
incorporates a journal bearing 36 such that the input and output
parts 33 and 34 of the elbow joint can rotate relative to each
other about the longitudinal axis 35' of the intermediate section
35 of the elbow joint. The input part 33 of the elbow joint is
joined to its associated section 37 of the laser beam guide by
means of a joint which includes another journal bearing 38. The
bearing 38 enables the input part 33 of the elbow joint to rotate
about the longitudinal axis 37' of the section 37 of the laser beam
guide. The output part 34 of the elbow joint is joined rigidly to
its associated section 39 of the laser beam guide. The bearings 36
and 38 provide for a universal action of the elbow joint.
The mirrors 31 and 32 are so positioned that when the longitudinal
axes 37', 35' and 39' of the sections 37, 35 and 39 of the laser
beam guide are co-planar, the mirrors 31 and 32 are parallel and at
an angle of 45.degree. to the longitudinal axes 37', 35' and 39' of
the sections 37, 35 and 39 of the laser beam guide. Thus these axes
form the optic axis of the optical system formed by the mirrors 31
and 32. A beam 40 of laser radiation entering the elbow joint along
the axis 37' of the section 37 of the laser beam guide will leave
the elbow joint along the axis 39' of the section 39 of the laser
beam guide whatever the relative positions of the input and output
parts 33 and 34 of the elbow joint.
For the above statement to be true, it is necessary for the
bearings 36 and 38 to be of high quality, and great care is needed
in the manufacture and assembly of the components of the elbow
joint. FIG. 4 shows a form of elbow joint in which these conditions
can be relaxed. The general principles of construction are the same
as those of the elbow joint which has been described already so the
construction of the elbow joint will not be described in detail
again, and those components which are similar to those in the elbow
joint already described are given the same reference numbers. The
two forms of the elbow joint differ in that instead of the mirrors
31 and 32 being accurately pre-aligned, one of them, in the
illustration the output mirror 32 although it can be either of
them, is mounted so that it can be moved about two perpendicular
axes, and there is provided a servo mechanism 41 which maintains
the alignment of the mirrors required to ensure that the laser beam
40 leaving the elbow joint does so along the axis 39' of the
section 39 of the laser beam guide whatever the relative positions
of the input and output parts 33 and 34 of the elbow joint. This
being so, the requirement for great precision in the construction
of the elbow joint, and in particular the journal bearings 36 and
38 can be relaxed. To provide the necessary input information for
the servo mechanism 41, any convenient form of laser beam position
sensor can be used such as a diaphragm 42 divided into quadrants 43
each of which has a temperature sensor 44 associated with it.
Although only three elbow joints, as described, are necessary to
provide a functional system, to accommodate manufacturing errors,
it is desirable to include an additional elbow joint in one of the
sections of the flexible laser beam guide 8. Alternatively, one of
the sections of the flexible laser beam guide 8 can be provided
with a telescopic joint.
The rotational capacity provided between the fixed and flexible
portions of the laser beam guide 8 and 9 repectively, by means of
the input part journal bearing of the elbow joint 12 and the
trunnions 6 enable the base plate 5 to move about an axis which is
coincident with the longitudinal axis of the fixed laser beam guide
9. Thus the required orientation of the operating laser beam in
relation to the piping 20 can be maintained whatever the
orientation of the axis of the piping 20 in a plane perpendicular
to the axis of rotation of the base plate 5.
* * * * *